1. Field of the Invention
The invention relates to the field of broadcast transmitting technology. In particular, it relates to an amplitude-modulated broadcast transmitter for various types of modulation, particularly DSB (double sideband), SSB (single sideband) and ISB (independent sideband).
A method and a corresponding device for generating an ISB transmitting signal are known from U.S. Pat. No. 4,955,072.
A method and a corresponding device for generating an SSB transmitting signal are known from EP 0,193,655 A1.
Various methods and corresponding devices for generating a DSB transmitting signal are described, for example, in the book "Taschenbuch der Hochfrequenztechnik" (Pocket book of radio-frequency engineering) (H. Meinke and F. W. Gundlach, Springer-Verlag Berlin/Heidelberg/New York 1968).
2. Discussion of Background
In broadcast transmitting technology working with amplitude modulation (AM), transmitters are used in which, of the two Sidebands produced by the modulation, either both (DSB=double sideband) or only one (SSB=single sideband) are transmitted. In addition, there is also the variant that the two sidebands carry different information items independently of one another (ISB=independent sideband). In the amplitude-modulated broadcast transmitters according to the prior art, DSB, SSB and ISB transmitters having different modulators in each case are used for the different types of modulation.
A method for generating an amplitude-modulated ISB transmitting signal and a device for carrying out the method is proposed in U.S. Pat. No. 4,955,072. It is based on the single-sideband modulation method disclosed in EP 0,193,655 A1, and the corresponding single sideband modulator.
An SSB signal or an ISB signal is no longer purely amplitude modulated but additionally also phase modulated. A device must therefore be provided for the required phase modulation. The two independent AF signals are split into their orthogonal components in the said ISB method. From these orthogonal components and a carrier amplitude, component sums are formed in such a manner that a signal is produced which contains the information from one AF signal in the lower sideband and that from the second AF signal in the upper sideband. This signal is then supplied to an amplitude processor or a cyclic sampler. The amplitude processor supplies an amplitude signal which, after suitable conversion, can be used for the anode modulation of the transmitting tube. From the samples of the sampler, a phase signal is obtained by clipping or null detection. After suitable frequency conversion, this phase signal is used for the grid modulation of the transmitting tube. It thus modulates the carrier oscillation of the transmitting signal.
In the said SSB method and the corresponding device, a phase-independent amplitude signal and an amplitude-independent phase signal is generated in similar manner from an AF signal.
However, it is common to these various methods and devices that they can in each case only be used for one type of modulation.